Effects of Inorganic Passivators on Gas Production and Heavy Metal Passivation Performance during Anaerobic Digestion of Pig Manure and Corn Straw

Abstract

The treatment of livestock manure caused by the expansion of the breeding industry in China has attracted wide attention. Heavy metals in pig manure can pollute soil and water and even transfer to crops, posing harm to humans through the food chain. In this study, corn straw was selected as the additive and introduced into the anaerobic digestion. Sepiolite (SE), ferric oxide (Fe2O3), attapulgite (AT) and ferric sulfate (FeSO4) were used as passivators to compare the effects of these inorganic passivators on gas production and passivation of heavy metals during the process of the anaerobic digestion. When the dry mass ratio of pig manure to straw is 8:2, the gas production efficiency is optimal. SE, AT and ferric sulfate have a much stronger ability to improve gas production performance than Fe2O3. The total gas production increased by 10.34%, 6.62% and 4.56%, and the average methane production concentration increased by 0.7%, 0.3% and 0.4%, respectively. The influence of SE, AT and ferric sulfate on the passivation of heavy metals is much better than Fe2O3, and the fractions in biological effective forms of Cu and Zn reduced by 41.87 and 19.32%, respectively. The anaerobic digestion of mixed materials is conducive to the gas production and the passivation of heavy metals. Therefore, SE, AT and ferric sulfate are selected as composite passivators, and the optimal ratio of inorganic composite passivators i: AT 7.5 g/L, ferric sulfate 5 g/L and SE 7.5 g/L, according to the results of orthogonal experiments. This study can provide a theoretical basis for the safe application of biogas fertilizers.

Effects of Magnetic Biochar Addition on Mesophilic Anaerobic Digestion of Sewage Sludge

“…For measurements of TS and VS of sewage sludge, the sewage sludge was placed into a constant temperature drying oven for drying at 105 • C, and then placed in a muffle furnace at 600 • C for 2 h. The TS and VS were measured by the differential weight method. The sCOD was determined by the potassium dichromate digestion method, the concentration of soluble protein was determined by ultraviolet spectrophotometry using bovine serum protein as standard, and the concentration of soluble polysaccharides was determined by the phenol-sulfuric acid method [4,24]. The concentrations of VFAs (mainly acetic acid, propionic acid, n-butyric acid, iso-butyric acid, n-valeric acid, and iso-valeric acid) were measured using a gas chromatograph equipped with a flame ionization detector (Agilent 7890A, Santa Clara, CA, USA).…”

“…Therefore, the proper treatment technology for sewage sludge is essential. So far, anaerobic digestion (AD) is a relatively stable and extensively applied technology for treating sewage sludge, food wastes, and animal manure [3,4]. AD includes four stages: hydrolysis, acidification, acetogenesis, and methanogenesis [5].…”

Changes in Soil Chemical Properties and Rhizosphere Bacterial Community Induced by Soil Amendments Associated with Reduction in Cadmium Accumulation by Rice

“…Inorganic and organic amendments such as quicklime [12], apatite [11], commercial MgO-CaO-SiO 2 conditioner [13], biochar [4], and organic fertilizer [14] have been commonly utilized to immobilize and minimize Cd bioavailability in soils. However, the remediation mechanisms of various soil amendments for soils contaminated with Cd are quite different [15]. For example, biochar is a type of carbonaceous product of materials from a feedstock by pyrolysis at elevated temperatures under low or no oxygen conditions [16].…”